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Rivers and other bodies of water form
natural boundaries to human activity
Bridge design is driven by
o Economic need
o Projection of political and military might
o Doing something in a new creative way
Why did the stone age come about after the norm of wood bridges
The wood would rot
The Romans used bridges to
o Project military power
o Demonstrate their political might
o Carry clean water to their cities
The late 1800s saw two major changes
o Refinements to steel making; allowing steel with different properties (hardness, strength, durability)
The romantic notions of the “master builder”, bridges were no longer just structures, but monuments to the individual who planned and built them
What are the basic requirements for a bridge?
Handle the traffic, meet economic needs, withstand the environmental load and be aesthetically pleasing
Building a bridge requires an understanding of
The forces acting on it and the loads
What are the forces acting on a bridge?
Tension, compression, shear and torsion
What are the loads on a bridge?
Dead, live and environmental
What is a dead load?
The bridges own load
What is a live load?
The weight of traffic
What is an environmental load?
Forces exerted by wind, water, etc.
Static equilibrium occurs when
When an object is at equilibrium and rest
What is static force?
A constant force applied to a stationary object
What is compression?
A static force that tries to squeeze a material together to make it shorter
What is tension?
A static force that tries to stretch or pull apart a material to lengthen it
What is shear?
A static force that tries to slide the material apart in opposite directions
What is torsion?
A static force that tries to rotate the material in opposite directions
Wht are the six major types of bridges?
· Beam
· Truss
· Cantilever
· Arch
· Suspension
· Cable-stay
Characteristics of a simple beam bridge
Oldest type and still used, One or more beams (called decks) span the area between abutments or piers, Commonly used for short distances because they have no built-in supports
What is a deck?
Roadway supporting the live load
What is an abutment?
The supports at the end of a bridge
What is a pier?
The supports between the abutments mid-stream
What is a truss beam?
Uses a triangle-shaped design, The beams work together to spread out the load, Simplest modification to the simple beam design
What is a cantilever?
Structures that are anchored at only one end while the other end projects horizontally into space. Combines the truss with the concept of a lever; balances one side of its truss with the other
Characteristics of an arch bridge
It greatly reduces the ability of the beam to flex; little or no tensional force is generated, Distributes compression across and down the arch; it is always pushing in on itself, Abutments have to be built very strong because they will carry all of the weight and all of the forces
Characteristics of a cable-stayed bridge
The bridge’s deck is directly suspended from cables that are under tension from the dead load, Cables run directly from the tower to the deck, forming a fan-like pattern
Characteristics of a suspension bridge
The cable from the beam are connected to another cable, The long cable is strung over the towers and anchored on both sides, The smaller cables are hung from the main cables and connect to the deck
The first bridges were made out of
Natural material
What requirements make bridge building difficult?
Its required dimension, its traffic load, the body of water it spans, other environmental issues
How do you address the special requirements in making a bridge?
Understanding the art science and engineering, choosing the best material for the job and selecting a supportive bridge design
